1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to an electroluminescence device made using a silicon phosphor and an electrode with nanotips.
2. Description of the Related Art
The generation of light from semiconductor devices is possible, regardless of whether the semiconductor material forms a direct or indirect bandgap. High field reverse biased p-n junctions create large hot carrier populations that recombine with the release of photons. For silicon devices, the light generation efficiency is known to be poor and the photon energy is predominantly around 2 eV. The conversion of electrical energy to optical photonic energy is called electroluminescence (EL). Efficient EL devices have been made that can operate with small electrical signals, at room temperature. However, these devices are fabricated on materials that are typically not compatible with silicon, for example type III-V materials such as InGaN, AlGaAs, GaAsP, GaN, and GaP. An EL device built on one of these substrates can efficiently emit light in a narrow bandwidth within the visible region, depending on the specific material used. Additionally, type II-VI materials such as ZnSe have been used. Other type II-VI materials such as ZnS and ZnO are known to exhibit electroluminescence under ac bias conditions. These devices can be deposited onto silicon for use in light generating devices if special (non-conventional) CMOS processes are performed. Other classes of light emitting devices are organic light emitting diodes (OLEDs), nanocrystalline silicon (nc-Si), and polymer LEDs.
A simple and efficient light-emitting device compatible with silicon, and powered by a dc voltage would be desirable in applications where photonic devices (light emitting and light detecting) are necessary. Efficient silicon substrate EL devices would enable a faster and more reliable means of signal coupling, as compared with conventional metallization processes. Further, for intra-chip connections on large system-on-chip type of devices, the routing of signals by optical means is also desirable. For inter-chip communications, waveguides or direct optical coupling between separate silicon pieces would enable packaging without electrical contacts between chips. For miniature displays, a method for generating small point sources of visible light would enable simple, inexpensive displays to be formed.
J. Ruan et al. have proposed a structure of nano silicon superlattice light emission devices, formed from a multilevel of nano-silicon/oxide layers. The radiation center is the Si═O bonds. However, voltage pulses with high alternative polarities are required to generate electron-hole pairs.
Polman et al. have proposed doping silicon-based materials with Erbium (Er), to a density in the order of 1019/cm2 of Er. The silicon-based materials can be pure Si, silicon oxide, doped silicon oxide, or glasses. This density of Er requires a co-doping of oxide to increase the Er solid solubility in Si. However, in order for the Er radiation centers to generate light, high-energy electrons and holes must be generated and injected into the Er-doped material.
It would be advantageous if an EL device could be fabricated, that would be suitable for low-power, high-density, large-scale IC applications.
It would be advantageous if an EL device could be practically fabricated using conventional Si CMOS processes. It would be advantageous if these EL devices could be operated without large alternating polarity pulses or high-energy electron injections.